| Message ID | 20200507185608.GA14779@embeddedor (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | d8238f9eb6e0c175c8b657af20164eef6b30c71c |
| Headers | show |
| Series | tools/testing: Replace zero-length array with flexible-array | expand |
On 5/7/20 12:56 PM, Gustavo A. R. Silva wrote: > The current codebase makes use of the zero-length array language > extension to the C90 standard, but the preferred mechanism to declare > variable-length types such as these ones is a flexible array member[1][2], > introduced in C99: > > struct foo { > int stuff; > struct boo array[]; > }; > > By making use of the mechanism above, we will get a compiler warning > in case the flexible array does not occur last in the structure, which > will help us prevent some kind of undefined behavior bugs from being > inadvertently introduced[3] to the codebase from now on. > > Also, notice that, dynamic memory allocations won't be affected by > this change: > > "Flexible array members have incomplete type, and so the sizeof operator > may not be applied. As a quirk of the original implementation of > zero-length arrays, sizeof evaluates to zero."[1] > > sizeof(flexible-array-member) triggers a warning because flexible array > members have incomplete type[1]. There are some instances of code in > which the sizeof operator is being incorrectly/erroneously applied to > zero-length arrays and the result is zero. Such instances may be hiding > some bugs. So, this work (flexible-array member conversions) will also > help to get completely rid of those sorts of issues. > > This issue was found with the help of Coccinelle. > > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html > [2] https://github.com/KSPP/linux/issues/21 > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org> > --- > tools/testing/selftests/nsfs/pidns.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/tools/testing/selftests/nsfs/pidns.c b/tools/testing/selftests/nsfs/pidns.c > index e0d86e1668c0..e3c772c6a7c7 100644 > --- a/tools/testing/selftests/nsfs/pidns.c > +++ b/tools/testing/selftests/nsfs/pidns.c > @@ -27,7 +27,7 @@ > #define __stack_aligned__ __attribute__((aligned(16))) > struct cr_clone_arg { > char stack[128] __stack_aligned__; > - char stack_ptr[0]; > + char stack_ptr[]; > }; > > static int child(void *args) > Thanks for the patch. I will pull this in for 5.7-rc6 thanks, -- Shuah
On Thu, May 07, 2020 at 01:04:14PM -0600, Shuah Khan wrote: > > > > diff --git a/tools/testing/selftests/nsfs/pidns.c b/tools/testing/selftests/nsfs/pidns.c > > index e0d86e1668c0..e3c772c6a7c7 100644 > > --- a/tools/testing/selftests/nsfs/pidns.c > > +++ b/tools/testing/selftests/nsfs/pidns.c > > @@ -27,7 +27,7 @@ > > #define __stack_aligned__ __attribute__((aligned(16))) > > struct cr_clone_arg { > > char stack[128] __stack_aligned__; > > - char stack_ptr[0]; > > + char stack_ptr[]; > > }; > > static int child(void *args) > > > > Thanks for the patch. I will pull this in for 5.7-rc6 > Thanks, Shuah. -- Gustavo
diff --git a/tools/testing/selftests/nsfs/pidns.c b/tools/testing/selftests/nsfs/pidns.c index e0d86e1668c0..e3c772c6a7c7 100644 --- a/tools/testing/selftests/nsfs/pidns.c +++ b/tools/testing/selftests/nsfs/pidns.c @@ -27,7 +27,7 @@ #define __stack_aligned__ __attribute__((aligned(16))) struct cr_clone_arg { char stack[128] __stack_aligned__; - char stack_ptr[0]; + char stack_ptr[]; }; static int child(void *args)
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org> --- tools/testing/selftests/nsfs/pidns.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)